Sealed lateral wellbore junction

ABSTRACT

The present invention relates to downhole drilling operations, and more particularly, to the completion of lateral boreholes. Apparatus ( 100 ) is provided comprising a tubular liner portion ( 108 ) for lining a portion of a lateral borehole adjacent an opening of a borehole into the lateral borehole. An end portion of said tubular liner portion ( 108 ) is provided with a flange element ( 102 ) having a curved surface for locating in abutment with an area of main borehole surrounding said opening. A method of using said apparatus ( 100 ) is also provided.

[0001] The present invention relates to downhole drilling operationsand, more particularly, to the completion of lateral boreholes.

[0002] One object of any lateral borehole completion operation is toprovide a means of preventing shale transfer between the main borehole(leg 1) and the lateral borehole (leg 2). It is particularly desirableto prevent the ingress of shale from the lateral leg, through thewindow, and into the main leg. A consequence of such an ingress can be aplugging of production.

[0003] The problem of providing an adequate sealing of lateral boreholesduring a lateral completion operation is discussed in the Society ofPetroleum Engineers (SPE) paper 57540. The paper provides a solution tothe problem, namely the MX sleeve or multi-lateral Tie Back Insert(MLTBI as it was originally known). Whilst this proposed system may beoperated effectively, it does not allow fill re-entry to both the mainborehole (leg 1) and the lateral borehole (leg 2). Although the lateralborehole is mechanically accessible, the main borehole is merelyhydraulically accessible. Modification to the proposed system may allowmechanical access to the main borehole as well as the lateral borehole,but this access would be very limited. It is of course desirable toprovide full bore access to both legs so as to allow unrestricted use ofconventional downhole equipment.

[0004] A further solution is the “hook” hanger (or liner) systemdiscussed in U.S. Pat. No. 5,477,925. With reference to FIG. 1 of theaccompanying drawings, it will be understood that the aforementionedhook hanger system comprises a hook liner 2 of a generally cylindricalshape. The liner 2 is provided with a preformed opening 4. The geometryof the opening 4 is such that, when a lower end 6 of the liner 2 haspassed through a casing window and into an associated lateral borehole,said opening 4 can be aligned in such a way as to provide fullmechanical access to the portion of main borehole located downhole ofthe main/lateral junction. More specifically, the liner 2 can bearranged so as to project from the lateral borehole with the opening 4spanning the main borehole and facing downhole.

[0005] In addition to the opening 4, two ribs 8 are locateddiametrically opposite one another on the external cylindrical surfaceof the liner 2. Each rib 8 extends helically along the length of theliner 2 and, in use, undertakes a “hooking”role wherein the portion ofcasing adjacent the window is engaged by each rib 8 so as to ensure thatthe opening 4 is located correctly.

[0006] The prior art hook hanger system is employed once a window mill10 and whipstock 12 have been used, in a conventional manner, to cut awindow 14 in the casing 16 of a main borehole (as shown in FIGS. 2 and3). A lateral borehole is then drilled from the window 14 intosurrounding formation. The aforementioned system is then used to lineand thereby seal the lateral borehole. This is achieved by attaching atubing string (by means of a crossover element) to the lower end 6 ofthe liner 2 and running the tubing string (followed by the liner 2) intothe lateral borehole. Conveying of the tubing string (not shown) throughthe lateral borehole is preferably assisted by means of a bent joint.Once the tubing string has been fully deployed in the lateral borehole,the lower end 6 of the liner 2 is passed through the window 14. The ribs8 then locate against the window profile.

[0007] Entry into the lined lateral is achieved using a stringcomprising a further bent joint and suitable guide means. The guidemeans may be a mule shoe giving an orientation of the leg on thebullnose relative to the bent joint entry to either leg 1 (i.e. the mainborehole) or leg 2 (i.e. the lateral borehole).

[0008] With regard to entry into the portion of main borehole locatedbelow the main/lateral junction, it will be noted that the widestsection 18 of the casing window 14 extends for only a relatively shortdistance downhole. It is through this widest section 18 that the tubingstring and lower end 6 of the liner 2 is run. However, it will beappreciated that, in order to ensure adequate clearance for insertionthrough the window 6, the liner 2 must be somewhat narrower than saidwindow section 18. As a result, an undesirably restrictive lateralborehole can result.

[0009] Embodiments of the present invention will now be described withreference to the accompanying drawings, in which:

[0010]FIG. 1 is a schematic perspective view of a prior at hook hangersystem;

[0011]FIG. 2 is a schematic cross-sectional view of conventional milland whipstock cutting a casing window;

[0012]FIG. 3 is a schematic perspective view of the casing window ofFIG. 2;

[0013]FIG. 4 is a schematic perspective view of a first embodiment ofthe present invention;

[0014]FIG. 5 is a schematic perspective view of a lateral liner portionof the first embodiment;

[0015]FIG. 6 is a schematic perspective view of a second embodiment ofthe present invention;

[0016]FIG. 7 is a partial cross-sectional view of the first embodimentlocated in a final position adjacent a casing window;

[0017]FIG. 8 is a partial cross-sectional view of a third embodiment ofthe present invention located in a final position adjacent a casingwindow;

[0018]FIG. 9 is a schematic perspective view of a fourth embodiment ofthe present invention;

[0019]FIG. 10 is a schematic perspective view of a fifth embodiment ofthe present invention;

[0020]FIG. 11 is a schematic partial internal view of the fifthembodiment;

[0021]FIG. 12 is a schematic perspective view of the fifth embodimentwithin a main borehole casing;

[0022]FIG. 13 is a schematic perspective view of the fifth embodimentlocated adjacent a main borehole window;

[0023]FIG. 14 is a schematic part cross-sectional view of a mill andwhipstock system for cutting a preferred window profile;

[0024]FIG. 15 is a schematic perspective view of the preferred window ofFIG. 14;

[0025]FIG. 16 is a table of procedural steps for completing a lateralborehole;

[0026] FIGS. 17 to 19 schematically show a flange liner being run into alateral borehole which has not been provided with an undercut;

[0027]FIGS. 20 and 21 schematically show a flange liner being run into alateral borehole which has been provided with an undercut;

[0028]FIG. 22 schematically shows window and deployed flange linerpositions relative to a widetrack whipstock;

[0029]FIG. 23 schematically shows window and deployed flange linerpositions relative to a gauge max whipstock;

[0030]FIGS. 24 and 25 schematically show a sixth embodiment of thepresent invention comprising a collapsed lateral liner portion; and

[0031]FIGS. 26 and 27 schematically show use of the fourth flange linerin an eccentric wellbore casing.

[0032] A first embodiment 100 of the present invention is shownschematically in the perspective view of FIG. 4. The first embodiment100 may be termed a “flange” liner since it comprises a flange partconstructed from a tubular element 102. The tubular element 102 isprofiled so as to enable its diameter to be accommodated within aslightly larger tubular (i.e. a main borehole casing). An uphole end 104of the tubular element 102 is cylindrical in shape, whereas the portionof tubular element 102 downhole of said uphole end 104 is merely partcylindrical (i.e. open on one side). More specifically, said uphole end104 is provided with a part spherical node 105 which, in use, assists incentralising the tubular element 102 within a main borehole regardlessof the angle of said element 102 to said main borehole. Also, thetubular element 102 is provided with an elliptical aperture 106. Theaperture 106 is elongate and extends along the part cylindrical portionof the tubular element 102.

[0033] The aperture 106 receives a lateral liner portion 108 (see FIG.5) which is attached to the tubular element 102 by means of welding. Thelateral liner portion 108 is provided with a flange 110 at the endsecured to the tubular element 102 so as to assist with its correctlocation relative to said element 102. The lateral liner portion 108 isinserted through the tubular aperture 106 and welded so that the flange110 abuts the interior surface of the tubular element 102. As analternative arrangement, the flange 110 may be secured to the exteriorsurface of the tubular element 102. In a development of the flange liner100, FIG. 6 shows a second embodiment 112 of the present inventionwherein a ring seal element 114 has been provided on the externalsurface of the tubular element 102 about the lateral liner portion 108.The seal element 114 can be bonded to said external surface by means ofan appropriate adhesive or retained within a channel or groove definedin or on said surface. In use, the seal element 114 abuts the mainborehole casing and encircles the casing window so as to assist inpreventing fluid flow between the lateral borehole and the regionlocated between the main borehole casing and the tubular element 102.

[0034] Each flange liner 100,112 is sized in view of the main andlateral boreholes with which it is to be used. The diameters and radiiof each liner 100,112 are critical in as much as a close fit of linercomponents 102,108 relative to the main and lateral boreholes isdesirable in order to eliminate shale ingress into the main boreholecasing. With this in mind, it should be understood that in use, eachflange liner 100,112 is intended to finally locate with the lateralliner portion 108 projecting into the lateral borehole. Whilst in thisposition, the part spherical node 105 should abut the full circumferenceof the internal surface of the main borehole casing and an area oftubular element 102 encircling the lateral liner portion 108 should alsoabut an area of said internal surface encircling the casing window.

[0035] A schematic part cross-sectional view of the first embodiment 100is shown in FIG. 7 located in the above described final position. Itwill be seen that the downhole edge 116 of the casing window is inabutment with both the external curved surfaces of the tubular element102 and lateral liner portion 108. As such, said downhole edge 116 maysupport the weight of the flange liner 100 and prevent further movementthereof down the main and lateral boreholes.

[0036] However, each flange liner 100,112 is primarily sized so as toallow it to run smoothly through the main borehole casing prior toachieving the ideal final position indicated above. Accordingly, eachflange liner 100,112 must be sized so as to be deployable through theradii of curvature commonly found in well bores (for example, up to15°/100′ for a 7″ casing—but not limited to such cases). For a 7″ mainborehole casing, the lateral liner portion 108 may be provided as a4{fraction (1/2)}″ tubing.

[0037] In order to assist with running the aforementioned flange liners100,112 in hole and to minimise deflection of lateral lining attached tothe downhole end of the lateral liner portion 108, one or more flexjoints (such as a knuckle joint) are located in said lateral liner. Itis particularly desirable to locate a flex joint adjacent said downholeend of the lateral liner portion 108. The use of means for allowingbending of said lateral lining (particularly that lining locatedadjacent liner portion 108) will reduce the possibility of laterallining collapse or, indeed, kinking or crimping of the flange liners100,112 themselves.

[0038] Despite the use of flex joints, the ideal dimensions of a flangeliner (from the view point of its final position as discussed above) maybe compromised by the need to run through a main borehole having, forexample, a particularly restrictive radius of curvature. In thesecircumstances, the main/lateral junction sealing characteristicsassociated with the flange liner alone may not be adequate. It may thenbe necessary to incorporate cementing port collars and external casingpackers in the lateral tubing string so that the area surrounding themain/lateral junction can be cemented if so desired. An effectivebarrier to shale ingress can be thereby created.

[0039] Although the two flange liners 100,112 described above arelocated in position adjacent a casing window by engagement of thedownhole window edge 116 (see FIG. 7) with both the tubular element 102and the lateral liner portion 102, a mechanical anchoring device shouldideally also be provided adjacent the uphole end 104 of the tubularelement 102. Such a device may be set with any appropriate means (forexample, string weight or hydraulics) and is particularly desirablesince it prevents uphole movement of a flange liner. However, it shouldbe appreciated that such a device may not be necessary in certaincircumstances (for example, in a relatively simple main/lateral junctionarrangement). Where an anchoring device is used, annular seal assembliesmay be provided (possibly as part of said device) adjacent the upholeend of the flange liner.

[0040] Also, as shown by the third embodiment 118 in FIG. 8, theaforementioned final position adjacent a casing window can be achievedby the engagement of a laterally extending protrusion 120 with adownhole edge of said window. The protrusion 120 extends laterally froma downhole portion of the tubular element 102 spaced downhole from thelateral liner portion 108. The protrusion 120 and tubular element 102form a hook shape having a generally downwardly facing opening forreceiving the downhole window edge as the third flange liner 118 ispressed down the main borehole.

[0041] A fourth embodiment 150 of the present invention is shown in FIG.9 of the accompanying drawings. The fourth flange liner 150 is providedas two discrete components 152,154. The first discrete component 152 islargely identical to the first flange liner 100 shown in FIG. 4 and ismanufactured in the same manner. The first component 152 may however bebased on the design of the second or third flange liners 112,118 (withthe same modifications as described hereinafter with relation to thefirst liner 100). The only difference between said first component 152and the first flange liner 100 is that said first component 152 has amodified uphole end 156 of the tubular element 158. The modified upholeend 156 is part cylindrical (rather fully cylindrical with a sphericalnode) and has an upper edge 160 for abutment with the second discretecomponent 154. A lateral liner portion 162 extends from an ellipticalaperture 164 in the tubular element 158.

[0042] The second discrete component 154 is an elongate cylindricalsleeve having a preformed window 166 which, in use, is aligned with thewindow provided in the main borehole casing. The preformed window 166 issubstantially the same size and shape as the main borehole window and,when in its final downhole position, locates on the opposite side of thetubular element 158 therefrom. An uphole end 168 of the second component154 is provided with a downhole facing shoulder 170 for pressingdownwardly on the upper edge 160 of the first discrete component 152.The shoulder 170 extends in a circumferential direction about the secondcomponent 154 and is axially located so that the aperture 164 of thefirst component 152 axially aligns with the preformed window 166 whenthe shoulder 170 and upper edge 160 abut one another. Angular alignmentof the aperture 164 and preformed window 166 is ensured by the abutmentof two longitudinally extending edges 172 of the first component 152with two longitudinally extending shoulders 174 on the second component154 (only one visible in the view of FIG. 9). The longitudinal edges 172of the first component 152 continue downwardly from the upper edge 160and the longitudinal shoulders 174 continue downwardly from the downholefacing shoulder 170. The two longitudinal shoulders 174 themselvescontinue downwardly into a mule shoe profile 178 which, in use, can bereceived in a mating profile within the main borehole casing so as tocorrectly orientate the flange liner 150 and ensure that the lateralliner portion 162 aligns with the main borehole window.

[0043] The uphole end 168 of the second component 154 is provided withanchor and seal means (not shown). The downhole end of the secondcomponent 154 is provided with a seal sub 180 having circumferentialseal elements 182 and a bullnose/wireline entry guide 184 at itslowermost end. The second component 154 may also be provided with awhipstock/deflector latch profile located between the seal sub 180 andthe preformed window 166 so as to assist with depth and orientationfinding.

[0044] In use, the fourth flange liner 150 is run downhole with firstcomponent 152 axially displaced so that the lateral liner portion 162 islocated substantially below the second component 154. This arrangementallows the liner 150 to locate within the internal diameter of the mainborehole casing. The liner portion 162 (or attached lateral linertubing) preferably runs in contact with the main borehole casing sothat, as said portion 162 approaches the main borehole window and theliner 150 is appropriately orientated by the aforesaid means, the linerportion 162 (or attached tubing) tends to spring into the main boreholewindow. Biasing means may alternatively be provided for biasing theliner portion 162 (or attached liner tubing) into the window. The firstcomponent 152 then locates in the main borehole window as described inrelation to FIG. 7. The second component 154 concurrently runs downholeso that the preformed window 166 aligns with the aperture 164 and themain borehole window. In so doing, the shoulder 170 abuts the upper edge160 and presses the lateral liner portion 162 firmly into the lateralborehole. The outer diameter of the second component 154 issubstantially identical to the inner diameter of the tubular element158. Also, the outer diameter of the tubular element 158 issubstantially identical to the inner diameter of the main boreholecasing, Thus, the presence of the second component 154 adjacent the mainborehole window ensures that the tubular element 158 is pressed firmlyagainst the internal surface of the casing. Indeed, the tubular element158 is firmly squeezed between the second component 154 and the mainborehole casing so as to provide a good seal about the main/lateraljunction.

[0045] As the second component 154 aligns with the main borehole window,the seal sub 180 locates in a Polished Bore Receptacle (PBR) securedbelow the window within the main borehole.

[0046] It may be preferable to run the flange liner 150 downhole withouta full length of lateral liner tubing attached to the lateral linerportion 162. This may be the case even though said liner tubing isprovided with one or more flex joints. It may therefore be desirable toprovide the downhole end of the lateral liner portion 162 with aninwardly projecting flange (i.e. a landing profile). The liner 150 maythen be located in a main borehole window prior to the running of alateral liner tubing through the lateral liner portion 162. The lateralliner tubing may be provided with a profile for making with the flangeon the lateral liner portion 162.

[0047] A fifth embodiment of the present invention is shown in FIGS. 10and 11. The fifth flange liner 200 is identical to the fourth flangeliner 150 except for the provision of a landing profile 202 (asmentioned above) on the downhole end of the lateral liner portion 204,the provision of a ring seal element 205 (as described in relation tothe second flange liner 112 of FIG. 6) and the provision of a guidepin/slot system for ensuring the correct orientation of the firstdiscrete component 206 relative to the second discrete component 208.The guide pin/slot system comprises two elongate slots 210 (only one ofwhich is visible in the view of FIG. 10) along a length of the secondcomponent 208. The guide system further comprises two guide pins 212projecting from the inner surface of the uphole end of the tubularelement 214. In use, the fifth flange liner 200 is run in whole with thetwo guide pins 212 slidably located in the elongate slots 210. Thus, theguide pin/slot system allows relative axial movement between the firstand second discrete components 206, 208 without relative rotationalmovement therebetween (see FIGS. 12 and 13). In an alternativearrangement, guide slots may be provided in the tubular element 214 withcooperating guide pins being provided on the second discrete component208.

[0048] As described in relation to the fourth flange liner 150, theuphole end of the second component 208 is provided with anchor means 216and seal means 218.

[0049] A schematic internal view of the fifth flange liner 200 is shownin FIG. 11. It will be seen that the interior of the second discretecomponent 208 comprises an internal latch profile 220 at a downhole endthereof for receiving a deflector 222. In use, the deflector 222 isemployed to deflect the subsequently run lateral liner tubing into thelateral borehole. The lateral liner tubing is preferably conveyed inwhole with an acidizing string made up internal to said liner. Theacidizing string is provided with wrapped screens such that acidizing offormation can be carried out concurrently. The use of an acidizingstring can be adapted to use with all the flange liners mentionedherein. Once the lateral liner tubing has been located within thelateral borehole, the acidizing string may be retrieved and thedeflector 222 recovered from the flange liner 200 so as to allow fullaccess to the main borehole below the main/lateral junction.

[0050] Where size is not a constraint, the lateral borehole need not bedrilled immediately after cutting the main borehole window andsubsequently milling rat hole (i.e. a pilot hole). Instead, the flangeliner 200 may be deployed as previously described and the lateralborehole drilled off the deflector 222. The completion string i.e. thelateral liner tubing) and acidizing string may then be run into thelateral borehole. The acidizing string, deflector 222 and any debrisbarrier may then be recovered.

[0051] The aforementioned flanged liners may be used with main boreholewindows having standard geometries (for example, the casing window 14shown in FIG. 3). Such windows may include Widetrack, Gauge Max, andpossibly even Extended Gauge, all being predominantly variations onTrackmaster windows produced using multi-ramp whipstock profiles. Themost appropriate form of window may be one which is an extended gaugewidetrack. Such a window comprises a standard cut out, extendedwidetrack (maximum width section as produced with Gauge Max, but havinga shorter length) and a runout which causes tapering at the bottom ofthe window, but which allows mill exit into formation when cutting a rathole (i.e. a pilot hole for the drilling assembly).

[0052] A casing window particularly suited to use with theaforementioned flange liners is shown in FIGS. 14 and 15 of theaccompanying drawings. Using a Trackmaster mill 300 and whipstock 302system having controlled gauge, it is possible to provide a window 304having a maximum width 306 substantially equal to the mill 300 maximumdiameter for the majority of the window length. This window profile isachieved by the whipstock 302 having a concave height which remainsessentially constant. As a result, the mill 300 travels from adjacentthe top of the window to adjacent the bottom of the window whilstcutting with its maximum diameter. This may be contrast with the priorart hook hanger system wherein the maximum width of the window 14extends over a very short length. Consequently, the location of themaximum window width is more difficult to predict in the prior artsystem and complicates installation of the completion assembly.

[0053] With the window profile shown in FIGS. 14 and 15, it is possibleto drill off the whipstock 302 into the surrounding formation—not havingexited into the formation with the mill 300 when cutting the window 304.Drilling of the concave would necessitate use of a directional motorwith a bent housing orientated to drive the drilling bit into theformation. Alternatively, a drilling bit could be deflected into theformation using a deflector which has been installed so as to replacethe whipstock 302 used to mill the window 304. As a further alternative,the whipstock 302 could be anchored uphole of the position shown in FIG.14 so that the lowermost ramp 308 of said whipstock 302 can be used todeflect the drilling bit through the window 304.

[0054] A completion process chart is provided in FIG. 16 of theaccompanying drawings wherein the steps to be taken in completing anatural borehole (leg 2) with an undercut (without a bent joint) orwithout an undercut (with a bent joint) are indicated. The concurrentrunning of a lateral tubing string 400 and the first flange liner 100through a window 402 provided in a main borehole casing 404 (between thedotted lines labelled with reference numeral 406) is shown in the queuesequences of FIGS. 17 to 19 and FIGS. 20 to 21. The first sequence shownin FIGS. 17 to 19 relate to the completion of lateral borehole with noundercut (i.e. through use of a bent joint). The second sequence shownin FIGS. 20 to 21 show the completion of a lateral borehole with anundercut (i.e. through use of a deflector 408). In each sequence, theflange liner 100 is connected to the lateral liner tubing 400 by meansof a flex joint 410.

[0055] The completion operations summarised in the aforementioned twosequences make use of a widetrack whipstock. A plan view of thedeflecting surface of said widetrack whipstock 412 is shown in FIG. 22wherein the location of the cut window 402 in relation to a fullydeployed flange liner 100 is shown by means of the aforementioned dottedlines 406. Cross-sectional views of the flange liner 100 at variouslongitudinal positions along its length are also shown in FIG. 22wherein the lateral position of said flange liner relative to thelongitudinal axis 414 of the casing 404 is presented. By way ofcontrast, FIG. 23 shows a gauge max whipstock 416 with the associatedwindow and flange liner 100 positions being indicated by theaforementioned dotted lines 406. It will be appreciated that the dottedlines 406 relate to a different window to the window 402 referred to inrespect of FIGS. 17 to 22. Cross-sectional views of the flange liner 100are also shown in FIG. 23 in a similar manner as shown in FIG. 22. Asixth embodiment 500 of the present invention is shown, in part, inFIGS. 24 and 25. The sixth flange liner 500 is identical to the fifthflange liner 200 except that the lateral liner portion 502 is formed ina collapsed state so as to allow the flange liner to locate within themain borehole casing. It will be noted that FIGS. 24 and 25 merely showa first discrete component 504 for replacing the first discretecomponent 206 of the fifth flange liner 200. A second discrete component(corresponding to the second discrete component 208 of the fifth flangeliner 200) in respect of the sixth flange liner 500 is not shown inFIGS. 24 and 25.

[0056] The collapsed lateral liner portion 502 may be resilientlydeformed as shown in FIGS. 24 and 25 so that the illustrated deformedshape is retained by means of lateral force applied by the chasing ofthe main borehole. Thus, in these circumstances, once the first discretecomponent 504 locates adjacent the main borehole chasing, the lateralliner portion 502 will tend to spring back to its original tubularshape. In this regard, the lateral liner portion 502 may be manufacturedfrom titanium or any suitable alloy. Alternatively, the collapsedlateral liner portion 502 may be reformed into a tubular shape bymechanical, hydraulic, explosive or any other suitable means.

[0057] The present invention is not limited to the specific embodimentsand methods described above. Alternative arrangements and suitablematerials will be apparent to the reader skilled in the art. Forexample, any one of the aforementioned flange liners may be used inconjunction with a main borehole casing which has been provided with aneccentric joint. Such an arrangement is shown in FIGS. 26 and 27 whereinthe fourth flange liner 150 is run through a portion of main boreholecasing having two overlapping internal diameters 602, 604.

[0058] Inventor comments in respect of the system shown in FIGS. 26 and27 are as follows:

[0059] Provide a joint of casing shaped like a gas lift mandrel (25 to30 feet in length). The window would be created or, better stillpreformed, at the lower most end of the eccentric part of the joint.There would be a MOLE like profile sub run below this joint for a depthand orientation datum point. The top most part of the eccentric jointwould house a sliding sleeve 154 with a preformed window 166 in it justslightly larger than the main borehole window.

[0060] Operation would be as follows—

[0061] 1) Drill 8½″ hole or larger to depth.

[0062] 2) Run 7″ casing with one or more Gas lift mandrel shapedeccentric joints (EJ) with MOLE equivalent profile subs below eachjoint.

[0063] 3) Orientate the EJ's to the desired azimuth (preferably highside).

[0064] 4) Cement the casing string in place (the ID and the EJ would belined with a compound that could be jetted away with a jet wash tool).

[0065] 5) Run the jet wash tool to remove the lining (perhaps even anacid soluble lining).

[0066] 6) Run the whipstock/deflector and latch into the MOLE sub, setthe packstock and drill ahead to depth.

[0067] 7) Run the lateral to completion with the saddle 152 and landoff. The running tool must extend into the lateral liner and it musthave a hydraulic and/or mechanical release mechanism so that is canwithstand pushing and pulling to get the completion to bottom. Atelescopic joint with a lock ring assembly above where the running toollocates may be used. Once the completion is landed and the running toolis released, pick up and use the completion running tool to close thetelescopic joint and drive home the saddle 152.

[0068] 8) Once the saddle 152 is seated, pull out of the hole and run inwith a tool to engage the sliding sleeve 154 and force it down tosandwich the saddle. The bottom of the sleeve may incorporate a latch tolock it into position.

[0069] 9) Move up and do the next lateral borehole.

1. Downhole apparatus for sealing a junction between a main borehole anda lateral borehole, the apparatus comprising a tubular liner portion forlining a portion of a lateral borehole adjacent an opening of a mainborehole into the lateral borehole, an end portion of said tubular linerportion being provided with a flange element having a curved surface forlocating in abutment with an area of main borehole surrounding saidopening.
 2. Downhole apparatus as claimed in claim 1, wherein saidcurved surface is part cylindrical.
 3. Downhole apparatus as claimed inclaim 1 or 2, wherein said flange element is elongate in shape and oneend thereof is cylindrical.
 4. Downhole apparatus as claimed in claim 3,wherein said cylindrical end comprises a part spherical portion. 5.Downhole apparatus as claimed in claim 3 or 4, wherein said cylindricalend is spaced from said tubular liner portion.
 6. Downhole apparatus asclaimed in claim 2, wherein said flange element is elongate in shape andone end thereof is provided with an edge profile, said downholeapparatus further comprising a cylindrical member having a projectionfor abutment with said edge profile.
 7. Downhole apparatus as claimed inclaim 6, wherein said cylindrical member is provided with an aperture inthe side thereof, said aperture being positioned so as to align withsaid tubular liner portion when said projection and edge profile are inabutment.
 8. Downhole apparatus as claimed in claim 7, wherein theexterior surface of said cylindrical member about said aperture isprovided with a seal element.
 9. Downhole apparatus as claimed in any ofclaims 6 to 7, wherein said flange element is secured to saidcylindrical member by means for permitting relative axial movementbetween said flange element and said cylindrical member without relativerotational movement therebetween.
 10. Downhole apparatus as claimed inclaim 9, wherein said means comprises a pin slidably located in a slot.11. Downhole apparatus as claimed in claim 10, wherein said pin isprovided on said flange element and said slot is provided on saidcylindrical member.
 12. Downhole apparatus as claimed in any of claims 9to 11, wherein said means for permitting relative axial movement permitsmovement of said flange element from a first position, wherein thelongitudinal axis of said tubular liner portion is substantially in linewith the longitudinal axis of said cylindrical member, to a secondposition, wherein said edge profile and shoulder are in abutment and thelongitudinal axis of said tubular liner portion extends at an angle tothe longitudinal axis of said cylindrical member.
 13. Downhole apparatusas claimed in any of the preceding claims, wherein the exterior surfaceof said flange element about said tubular liner portion is provided witha seal element.
 14. Downhole apparatus as claimed in any of thepreceding claims, wherein said tubular liner portion comprises foldedside walls so that, when unfolded, said tubular liner portion has acircular cross-section, and, when folded, said tubular liner portion hasa cross-sectional area of less magnitude than the area of said circularcross-section.
 15. A method of sealing a junction between a mainborehole and a lateral borehole, the method comprising the steps ofrunning the apparatus of any of the preceding claims down a mainborehole and locating the tubular liner portion within a lateralborehole.
 16. A method as claimed in claim 15, the method comprising thefurther step of pressing the flange element into abutment with an areaof main borehole surrounding an opening of the main borehole into thelateral borehole.
 17. A method as claimed in claim 16, wherein saidflange element is pressed by means of a cylindrical member.
 18. A methodas claimed in any of claims 15 to 16, the method comprising the step ofexpanding said tubular liner portion from a folded condition to anunfolded condition in which said tubular liner portion is generallycylindrical in shape.
 19. A method as claimed in any of claims 15 to 17,wherein said tubular liner portion is folded prior to running saidapparatus down the main borehole.